Sensor material providing an on / off switchable colour change

Abstract

According to an example aspect of the present invention, there is provided a material represented by the chemical formula (I) (M1'8-2aM2'a)(M''14-(4b / 3)M'''b)O24(X2-dcdX'n c-):M'''' (I) capable of providing an on / off switchable colour change when exposed to radiation at a specific wavelength. The invention also relates to a synthetic method for producing said material, and to the use of said material as an on-off switchable colour filter in various applications.

Description

SENSOR MATERIAL PROVIDING AN ON / OFF SWITCHABLE COLOUR CHANGE FIELD

[0001] The present invention relates to a material capable of providing an on / off switchable colour change when exposed to radiation at a specific wavelength.

[0002] The invention also relates to a synthetic method for producing said material, and to the use of said material as an on-off switchable colour filter, or security marker, in various applications. BACKGROUND

[0003] Hackmanite, which is a variety of sodalite material, is a natural mineral having the chemical formula of Na8Al6Si6O24(Cl,S)2. It has a unique character in being able to reversibly change its colour when exposed to radiation.

[0004] A synthetic hackmanite-based material can also be prepared, and the chemical formula adjusted, whereby also the behaviour of the material upon radiation can be changed. An example of such a synthetic material is described for example in WO 2022 / 269128, where it is used for detecting radiation.

[0005] Since the natural mineral has weaknesses, such as high variability in impurities causing uncontrollable performance, further modifications have been investigated to optimize the behaviour of the material when exposed to radiation. SUMMARY OF THE INVENTION

[0006] The invention is defined by the features of the independent claims. Some specific embodiments are defined in the dependent claims.

[0007] According to a first aspect of the present invention, there is provided a synthetic sensor material having a chemical formula resembling that of hackmanite.

[0008] According to a second aspect of the invention, there is provided a synthetic material capable of an on / off switchable change in absorbance and reflectance at a wavelength ranging at least from the visible region to the near-infrared (NIR) region of the electromagnetic spectrum.

[0009] According to a further aspect of the invention, there is provided a novel method for synthesizing said material.

[0010] The invention thus relates to a material represented by the chemical formula (I) (M1’8-2aM2’a)(M’’14-(4b / 3)M’’’b)O24(X2-dcdX’ c- n ):M’’’’ (I) capable of providing an on / off switchable colour change when exposed to radiation at a specific wavelength.

[0011] The invention also relates to a synthesis method for producing said material, and to the use of said material as an on-off switchable colour filter in various applications.

[0012] Significant advantages are achieved using said invention. Among others, a material has been prepared, which is capable of altering its energy level structure when exposed to radiation. The structural changes result in changes in the reflectance spectrum of the material. The material will, however, remain fully functional after these structural changes, and the changes are reversible.

[0013] These structural changes cause also a change in the visual appearance of the material, and make the material useful as an environmentally friendly, non-toxic, low-cost and reusable sensor material, e.g. for use as a security marker or switchable neutral density filter. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] FIGURE 1 shows a photo of an example material according to the invention with one side exposed to 302 nm UV and other side unexposed.

[0015] FIGURE 2 shows reflectance spectra a-h before and after 302 nm UV exposure for example compositions.

[0016] FIGURE 3 is a graphical image of the coloration rise for an example material under a 302 nm UV lamp.

[0017] FIGURE 4 is a graphical image of the colour fading for an example material in darkness at room temperature.

[0018] FIGURE 5 is a graphical image of the colour fading for an example material under 6400 lx white light.

[0019] FIGURE 6 is a graphical image of the colour fading for an example material when heating.

[0020] FIGURE 7 shows the results of repeated coloration-bleaching steps for an example material at room temperature. EMBODIMENTS

[0021] DEFINITIONS

[0022] In the present context, the term “spectrum” can be used to denote the spectrum of reflected, transmitted or detected light.

[0023] The term “sensor material” herein denotes a material, such as a material represented by Formula (I), altering its structure when exposed to radiation, causing a visible change in its appearance. Most typically, the chemical composition of the material stays the same also after the changes described herein.

[0024] The present disclosure relates to a synthetic sensor material represented by the chemical formula (I) (M1’ M2’ )(M’’ M’’’ )O (X c- 8-2a a 14-(4b / 3) b 24 2-dcdX’n ):M’’’’ (I)wherein M1’ represents a monovalent monoatomic cation of an alkali metal selected from Group 1 of the IUPAC periodic table of the elements, or any combination of such cations; M2’ represents zinc (Zn), a divalent monoatomic cation of an alkaline earth metal selected from Group 2 of the IUPAC periodic table of the elements, or a divalent transition metal from groups 4-12 of the IUPAC periodic table of the elements, or a combination of zinc with a divalent monoatomic cation of an alkaline earth metal selected from Group 2 of the IUPAC periodic table of the elements, or with any combination of such cations; M’’ represents a trivalent monoatomic cation of an element selected from Group 13 of the IUPAC periodic table of the elements, or any combination of such cations; M’’’ represents a monoatomic cation of an element selected from Group 14 of the IUPAC periodic table of the elements, or any combination of such cations; X represents an anion of an element selected from the halogens of Group 17 of the IUPAC periodic table of the elements, or any combination of such anions; X’ represents an anion of one or more elements selected from the chalcogens of Group 16 of the IUPAC periodic table of the elements, or any combination of such anions; and M’’’’ represents a dopant cation of an element selected from rare earth metals of the IUPAC periodic table of the elements, or from transition metals of the IUPAC periodic table of the elements, or of barium (Ba), strontium (Sr), thallium (Tl), lead (Pb), or bismuth (Bi), or any combination of such cations, or M’’’’ is absent; and a is a value of 0.001 – 4; b is a value of 0 – 10.5; c is a value from above 0 to 4, thus incorporating, among others, the values 1, 2, 3 and 4; d is a value limited by d*c extending from above 0 to 2; n is a value from above 0 to 4, thus incorporating, among others, the values 1, 2, 3 and 4.

[0025] In the Formula I mentioned above, preferred alternatives for M1’ are sodium (Na) and potassium (K), most suitably being Na. Similarly, preferred alternatives for M2’are zinc (Zn), magnesium (Mg) and a combination of Zn and Mg, M2’ most suitably being Zn.

[0026] A preferred alternative for M’’ is aluminium (Al), whereas a preferred alternative for M’’’ is silicon (Si).

[0027] A preferred alternative for X is chlorine (Cl), and a preferred alternative for X’ is sulphur (S).

[0028] In one embodiment, the material is doped with at least one transition metal ion. M’’’’ is such a dopant, but is preferably absent.

[0029] In a particularly preferred embodiment, the material has the following chemical formula (II): (Na8-2aZna)(Al14-(4b / 3)Sib)O24(Cl2-dcdSnc-) (II)

[0030] In either one of Formulae (I) and (II) above, the value for a is preferably 0.05–4, more preferably 0.001–3.9, even more preferably 0.1–1.0, most suitably 0.1–0.7. Independently, the value for b is, in turn, preferably 1–10, more preferably 6. Likewise, the value for c preferably is 2. The value for d is preferably 0.04–0.1, more preferably 0.05– 0.09. Also, independently, the value for n is preferably 2.

[0031] Examples of the material of either Formula (I) or Formula (II) may have one of the following formulae: Na Zn AlSiO Cl 0.05S2- 7.2 0.4 6 6 24 1.90 2 Na Zn 2- 6.8 0.6Al6Si6O24Cl1.880.06S2 Na Zn AlSiO Cl 0. 2- 6.8 0.6 6 6 24 1.86 07S2 Na6.8Zn0.6Al6Si6O24Cl1.820.09S22- Na Zn AlSiO C 2- 6.8 0.6 6 6 24 l1.800.10S2 Na Zn0.7Al6Si 2- 6.6 6O24Cl1.920.04S2 Na6.6Zn0.7Al6Si6O24Cl1.840.08S22- Na Zn AlSiO Cl 0.09S2- 6.6 0.7 6 6 24 1.82 2 Na Zn 2- 6.6 0.7Al6Si6O24Cl1.800.10S2 Na7.8Zn0.1Al6Si6O24Cl1.820.09S22- Na7.6Zn0.2Al6Si6O24Cl1.840.08S22- Na Zn AlSiO C 2- 7.4 0.3 6 6 24 l1.860.07S2Na7.2Zn0.4Al6Si6O24Cl1.860.07S22- Na7.0Zn0.5Al6Si6O24Cl1.880.06S22- Na Zn AlSiO C 2- 6.8 0.6 6 6 24 l1.880.06S2 Na Zn AlSiO Cl 0.06S2- 6.6 0.7 6 6 24 1.88 2 Na6.4Zn0.8Al6Si6O24Cl1.900.05S22- Na6.2Zn0.9Al6Si6O24Cl1.900.05S22- Na Zn AlSiO Cl 0.0 2- 6.0 1.0 6 6 24 1.90 5S2 Na6.0Zn0.9Mg0.1Al6Si6O24Cl1.880.06S22- Na 2- 6.0Zn0.8Mg0.2Al6Si6O24Cl1.880.06S2 Na Zn 2- 6.0 0.7Mg0.3Al6Si6O24Cl1.880.06S2 Na Zn M 2- 6.0 0.6 g0.4Al6Si6O24Cl1.880.06S2 Na6.0Zn0.5Mg0.5Al6Si6O24Cl1.880.06S22- Na Zn Mg A 2- 6.0 0.4 0.6 l6Si6O24Cl1.880.06S2 Na Zn Mg Al 2- 6.0 0.3 0.7 6Si6O24Cl1.880.06S2 Na6.0Zn0.2Mg0.8Al6Si6O24Cl1.880.06S22- Na Zn Mg AlSi 2- 6.0 0.1 0.9 6 6O24Cl1.880.06S2 Na Mg AlSiO Cl 2- 6.0 1.0 6 6 24 1.880.06S2 Na Zn Ca AlSiO Cl 0.06S2- 6.0 0.9 0.1 6 6 24 1.88 2 Na6.0Zn0.8Ca0.2Al6Si6O24Cl1.880.06S22- Na 2- 6.0Zn0.7Ca0.3Al6Si6O24Cl1.880.06S2 Na6.0Zn0.6Ca0.4Al6Si6O24Cl1.880.06S22- Na6.0Zn0.5Ca0.5Al6Si6O24Cl1.880.06S22- Na Z 2- 6.0 n0.4Ca0.6Al6Si6O24Cl1.880.06S2 Na Zn 2- 6.0 0.3Ca0.7Al6Si6O24Cl1.880.06S2 Na6.0Zn0.2Ca0.8Al6Si6O24Cl1.880.06S22- Na Zn Ca A 2- 6.0 0.1 0.9 l6Si6O24Cl1.880.06S2 Na Zn Sr Al 2- 6.0 0.9 0.1 6Si6O24Cl1.880.06S2 Na6.0Zn0.8Sr0.2Al6Si6O24Cl1.880.06S22- Na Zn Sr AlSi 2- 6.0 0.7 0.3 6 6O24Cl1.880.06S2 Na Zn Sr AlSiO 2- 6.0 0.6 0.4 6 6 24Cl1.880.06S2 Na Zn Sr AlSiO C 2- 6.0 0.5 0.5 6 6 24 l1.880.06S2 Na6.0Zn0.4Sr0.6Al6Si6O24Cl1.880.06S22- Na Zn Sr AlSiO Cl 80 2- 6.0 0.3 0.7 6 6 24 1.8 .06S2 Na6.0Zn0.2Sr0.8Al6Si6O24Cl1.880.06S22-Na6.0Zn0.1Sr0.9Al6Si6O24Cl1.880.06S22- Na6.8Zn0.6Al6Si6O24Br1.880.06S22- Na Zn AlSiO Br 0. 2- 6.6 0.7 6 6 24 1.88 06S2 Na Zn AlSiO Br 0.05 2- 6.4 0.8 6 6 24 1.90 S2 Na6.2Zn0.9Al6Si6O24Br1.900.05S22- Na6.0Zn1.0Al6Si6O24Br1.900.05S22- Na Z 2- 6.8 n0.6Al6Si6O24I1.880.06S2 Na6.6Zn0.7Al6Si6O24I1.880.06S22- Na Zn AlSiO 2- 6.4 0.8 6 6 24I1.900.05S2 Na Zn AlSiO I 0 2- 6.2 0.9 6 6 241.90.05S2 Na Zn AlSiO I 0.05 2- 6.0 1.0 6 6 241.90 S2 Na6.8Zn0.6Al6Si6O24F1.880.06S22- Na 2- 6.6Zn0.7Al6Si6O24F1.880.06S2 Na Zn A 2- 6.4 0.8 l6Si6O24F1.900.05S2 Na6.2Zn0.9Al6Si6O24F1.900.05S22- Na Zn AlSiO F 2- 6.0 1.0 6 6 24 1.900.05S2 Na Zn AlSiO Cl 0. 2- 6.8 0.6 6 6 24 1.88 06S Na Zn AlSiO Cl 0.06S2- 6.6 0.7 6 6 24 1.88 Na6.4Zn0.8Al6Si6O24Cl1.900.05S2- Na Zn 2- 6.2 0.9Al6Si6O24Cl1.900.05S Na6.0Zn1.0Al6Si6O24Cl1.900.05S2- Na6.8Zn0.6Al6Si6O24Cl1.880.12S3- Na Zn AlSiO Cl 0. - 6.6 0.7 6 6 24 1.88 12S3 Na Zn AlSiO Cl 0.10S- 6.4 0.8 6 6 24 1.90 3 Na6.2Zn0.9Al6Si6O24Cl1.900.10S3- Na Zn - 6.0 1.0Al6Si6O24Cl1.900.10S3 Na Zn AlS - 6.8 0.6 6 i6O24Cl1.880.12S Na6.6Zn0.7Al6Si6O24Cl1.880.12S- Na Zn AlSiO Cl 0.1 - 6.4 0.8 6 6 24 1.90 0S Na - 6.2Zn0.9Al6Si6O24Cl1.900.10S Na Zn A - 6.0 1.0 l6Si6O24Cl1.900.10S Na6.0Zn0.9Fe0.1Al6Si6O24Cl1.880.06S22- Na Zn 2- 6.0 0.8Fe0.2Al6Si6O24Cl1.880.06S2 Na6.0Zn0.7Fe0.3Al6Si6O24Cl1.880.06S22-Na6.0Zn0.6Fe0.4Al6Si6O24Cl1.880.06S22- Na6.0Zn0.5Fe0.5Al6Si6O24Cl1.880.06S22- Na Zn Fe AlSiO 2- 6.0 0.4 0.6 6 6 24Cl1.880.06S2 Na Zn Fe AlSiO Cl 0.06S2- 6.0 0.3 0.7 6 6 24 1.88 2 Na6.0Zn0.2Fe0.8Al6Si6O24Cl1.880.06S22- Na6.0Zn0.1Fe0.9Al6Si6O24Cl1.880.06S22-

[0032] Preferred examples of the material are: Na7.2Zn0.4Al6Si6O24Cl1.900.05S22- Na Zn AlSiO Cl 2- 6.6 0.7 6 6 24 1.920.04S2 Na6.6Zn0.7Al6Si6O24Cl1.840.08S22- Na6.6Zn0.7Al6Si6O24Cl1.820.09S22- Na 2- 6.6Zn0.7Al6Si6O24Cl1.800.10S2 Na Zn AlSiO Cl 0. 2- 7.8 0.1 6 6 24 1.82 09S2 Na7.6Zn0.2Al6Si6O24Cl1.840.08S22- Na Zn AlSiO Cl 0.0 2- 7.4 0.3 6 6 24 1.86 7S2 Na Zn 2- 7.2 0.4Al6Si6O24Cl1.860.07S2 Na7.0Zn0.5Al6Si6O24Cl1.880.06S22- Na6.8Zn0.6Al6Si6O24Cl1.880.06S22- Na.6Zn0.7Al 2- 6 6Si6O24Cl1.880.06S2

[0033] The material of Formulae (I) or (II) is an optically active material that is configured to be able to retain radiation exposed thereon to cause an on / off switchable change in its absorption and reflectance properties. The material is thus capable of providing an on / off switchable colour change ranging at least from the ultraviolet region to the near-infrared (NIR) region of the electromagnetic spectrum, when exposed to radiation at a wavelength from the UV region, or the X-ray region, or the gamma region, as well as when exposed to particle radiation. The initial color is restored upon heating or when exposed to white light for an extended range of time.

[0034] When radiating the material using radiation of the blue region, or a higher energy region, this may also cause a luminescence that may even persist as an afterglow. The above colour change will, however, reduce the intensity of the luminescence.

[0035] The material described herein is typically non-toxic and non-expensive.

[0036] The present disclosure also relates to a method for synthesizing the material of Formula (I) or (II), as described above, by ^ mixing and grinding one or more reagents containing X, one or more reagents containing X’, one or more reagents containing M2’ and one or more reagents containing M1’, M’’and M’’’, ^ mixing the components of the reagent mixture, and optionally heating, to obtain a precursor, ^ optionally further grinding the precursor, and ^ heating the precursor to 400–1300 ºC to obtain the final sensor material.

[0037] In an embodiment, the reagents containing X, X’ and / or M2’ are selected from molecules or salts of alkali metals, alkaline earth metals or transition metals with halogens or chalcogens, optionally containing oxide, preferably being selected from sodium chloride or bromide, potassium chloride or bromide, zinc chloride or bromide, magnesium chloride or bromide, or from the corresponding sulphates, for example by selecting sodium chloride (NaCl), sodium sulphate (Na2SO4) and zinc chloride (ZnCl2), typically in dried form.

[0038] The reagents containing M1’, M’’ and M’’’ may, in turn, be selected from oxides, salts, minerals or other molecules containing M1’, M’’ and M’’’, preferably from zeolites, one example being Zeolite A.

[0039] The amounts of reagents are typically selected based on the desired values for a, b, c and d of Formula (I) or (II).

[0040] In another embodiment the components of the reagent mixture are mixed together and thereafter optionally heated, e.g. in an air atmosphere, to a temperature of 400–1300 °C, preferably to a temperature of 650–750 °C, most suitably to a temperature of 680–720 °C. The pressure during heating is typically normal room pressure. However, since suitable reaction temperatures depend on the pressure, the limit for a sufficient temperature can be adjusted by adjusting the pressure, and correspondingly, the limits for a sufficient pressure can be adjusted by adjusting the temperature.

[0041] Preferably, the components are heated for 4–10h to obtain the precursor, more preferably for 4–6h.

[0042] In a further embodiment, the precursor is in the following step of the method, after an optional further grinding, heated in a reducing gas atmosphere (formed using e.g. H2, CO or NH3), for example to a temperature of 650–750 °C, preferably 680–720 °C, typically for 1–3 h. This step may, for example take place in a H2 / N2 gas atmosphere, such as under a flowing of a gas atmosphere of H2 / N2 at a volume ratio of 0.8–1.2 / 8.8–9.2. In an example, this heating or re-heating takes place under a flowing of an atmosphere of 10% H2+ 90% N2.

[0043] In another embodiment, the material is prepared using other protocols or systems such as microwave synthesis, microwave assisted synthesis, solvo- and hydrothermal syntheses, precipitation from liquid, layer deposition methods (e.g. pulsed laser deposition or atomic layer deposition), high-pressure synthesis or any other method that provides the suitable conditions described above where the material may be formed.

[0044] The material is preferably prepared in powder form and is typically also used in dry solid form. The particle size in the powder is typically from about 50 nm to 25 µm, preferably 5-10 µm, as measured by transmission electron microscopy. The measurements may be made based on the microscopy pictures with a watershed segmentation algorithm in the ImageJ program.

[0045] The invention also relates to the use of the above described material, or of the material prepared as described above, as an on-off switchable colour filter or pigment (or dye or colorant). Particularly, the material can be used in security markers, counterfeit markers, or in smart films or smart windows, particularly in security devices, medical applications or diagnostic applications.

[0046] This use is based on the fact that these types of materials, commonly called hackmanites, are altered in their electronic structure when exposed to radiation. The structural changes result in changes in the reflectance spectrum of the material. The material will, however, remain fully functional after these structural changes.

[0047] This colouration ability is reversible, and results in an environmentally friendly, non-toxic, low-cost and reusable material, e.g. for the applications suggested above.

[0048] It is to be understood that the embodiments of the invention disclosed are not limited to the particular structures, process steps, or materials disclosed herein, but are extended to equivalents thereof as would be recognized by those ordinarily skilled in the relevant arts. It should also be understood that terminology employed herein is used for the purpose of describing particular embodiments only and is not intended to be limiting.

[0049] Reference throughout this specification to “one embodiment” or “an embodiment” means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention. Thus, appearances of the phrases “in one embodiment” or “in an embodiment” in various places throughout this specification are not necessarily all referring to the same embodiment.

[0050] As used herein, a plurality of items, structural elements, compositional elements, and / or materials may be presented in a common list for convenience. However, these lists should be construed as though each member of the list is individually identified as a separate and unique member. Thus, no individual member of such list should be construed as a de facto equivalent of any other member of the same list solely based on their presentation in a common group without indications to the contrary. In addition, various embodiments and example of the present invention may be referred to herein along with alternatives for the various components thereof. It is understood that such embodiments, examples, and alternatives are not to be construed as de facto equivalents of one another, but are to be considered as separate and autonomous representations of the present invention.

[0051] Furthermore, the described features, structures, or characteristics may be combined in any suitable manner in one or more embodiments. In the following description, numerous specific details are provided, such as examples of lengths, widths, shapes, etc., to provide a thorough understanding of embodiments of the invention. One skilled in the relevant art will recognize, however, that the invention can be practiced without one or more of the specific details, or with other methods, components, materials, etc. In other instances, well-known structures, materials, or operations are not shown or described in detail to avoid obscuring aspects of the invention.

[0052] While the forgoing examples are illustrative of the principles of the present invention in one or more particular applications, it will be apparent to those of ordinaryskill in the art that numerous modifications in form, usage and details of implementation can be made without the exercise of inventive faculty, and without departing from the principles and concepts of the invention. Accordingly, it is not intended that the invention be limited, except as by the claims set forth below.

[0053] The verbs “to comprise” and “to include” are used in this document as open limitations that neither exclude nor require the existence of also un-recited features. The features recited in depending claims are mutually freely combinable unless otherwise explicitly stated. Furthermore, it is to be understood that the use of "a" or "an", i.e. a singular form, throughout this document does not exclude a plurality. EXAMPLES Example 1 – Synthesis of a material of Formula (I)

[0054] 0.072 g NaCl and 0.041319 g Na2SO4 are ground together in an agate mortar. 0.3918 g of dried ZnCl2 (1 h at 180°C) is added and the mixture is ground again. 0.7 g of zeolite A is added and the mixture is ground again. The mixture is poured into an alumina boat and heated at 700 °C for 5 h in air. After free cool-down to room temperature, the resulting product is ground and heated in a 10 % H2 + 90 % N2 gas atmosphere at 700 °C for 2 h. After free cool-down to room temperature, the resulting product is ground.

[0055] This example gives a material with stoichiometry Na 2 6.6Zn0.7Al6Si6O24Cl1.920.04S - 2 (Sample 6).

[0056] A similar recipe was used to prepare the materials of the following Table 1. Table 1.86.6 0.7 0 6 6 24 1.82 0.09 0.7 6 2 0.09 2 9 6.6 0.7 0 6 6 24 1.8 0.1 0.7 6 2 0.10 2 107.8 0.1 0 6 6 24 1.82 0.09 0.1 6 2 0.09 2 117.6 0.2 0 6 6 24 1.84 0.08 0.2 6 2 0.08 2 127.4 0.3 0 6 6 24 1.86 0.07 0.3 6 2 0.07 2 137.2 0.4 0 6 6 24 1.86 0.07 0.4 6 2 0.07 2 147 0.5 0 6 6 24 1.88 0.06 0.5 6 2 0.06 2 156.8 0.6 0 6 6 24 1.88 0.06 0.6 6 2 0.06 2 166.6 0.7 0 6 6 24 1.88 0.06 0.7 6 2 0.06 2 176.4 0.8 0 6 6 24 1.9 0.05 0.8 6 2 0.05 2 186.2 0.9 0 6 6 24 1.9 0.05 0.9 6 2 0.05 2 196 1 0 6 6 24 1.9 0.05 1 6 2 0.05 2 206 0.9 0.1 6 6 24 1.88 0.06 1 6 2 0.06 2 216 0.8 0.2 6 6 24 1.88 0.06 1 6 2 0.06 2 226 0.7 0.3 6 6 24 1.88 0.06 1 6 2 0.06 2 236 0.6 0.4 6 6 24 1.88 0.06 1 6 2 0.06 2 246 0.5 0.5 6 6 24 1.88 0.06 1 6 2 0.06 2 256 0.4 0.6 6 6 24 1.88 0.06 1 6 2 0.06 2 266 0.3 0.7 6 6 24 1.88 0.06 1 6 2 0.06 2 276 0.2 0.8 6 6 24 1.88 0.06 1 6 2 0.06 2 286 0.1 0.9 6 6 24 1.88 0.06 1 6 2 0.06 2 296 0 1 6 6 24 1.88 0.06 1 6 2 0.06 2 Example 2 – Performance of materials of Formula (I) Change in reflectance

[0057] The material of Sample 6, having the stoichiometry Na6.6Zn0.7Al6Si6O24Cl1.920.04S 2- 2 , and prepared as described in Example 1, was examined by collecting the material as a powder into a solid mass and exposing one side of the powder mass to UV radiation at 302 nm UV, and leaving the other side unexposed. The visible difference in colour between the two sides of the product is shown in Fig.1.

[0058] The difference can also be seen as a clear change in the background height in reflectance spectra, as shown for materials of Samples 1, 10, 11, 12, 13, 14, 15, and 16 of Table 1 in Fig.2 a-h.

[0059] The increase in coloration is shown in the graph of Fig. 3 for the same Sample 6 as prepared in Example 1. The colour fading for the same sample is, in turn,shown in Fig. 4. As the results show, the colour fades spontaneously in darkness in 2 – 4 days. White light (6400 lx) or heating can, however, be used to facilitate the return of the material to its initial state, as shown in Figs. 5 and 6, respectively. From these images it becomes clear that white light will cause a complete bleaching of the colour in about 20h, while heating the material will begin the bleaching process at a temperature of about 150 °C. Reversibility

[0060] The same Sample 6 as prepared in Example 1 was tested for repeatability of coloration and bleaching, to demonstrate the reversibility of the change in the material. A test was therefore carried out with 12 coloration-bleaching cycles. The results are shown in Fig.7, and demonstrate a good repeatability. INDUSTRIAL APPLICABILITY

[0061] The material described above can be used as an on-off switchable colour filter. Particularly, the material can be used in security markers, counterfeit markers, or in smart films or smart windows, particularly in security devices, medical applications or diagnostic applications. CITATION WO 2022 / 269128 A1

Claims

CLAIMS:

1. A synthetic sensor material represented by the chemical formula (I) (M1’8-2aM2’a)(M’’14-(4b / 3)M’’’b)O24(X2-dcdX’nc-):M’’’’ (I) wherein M1’ represents a monovalent monoatomic cation of an alkali metal selected from Group 1 of the IUPAC periodic table of the elements, or any combination of such cations; M2’ represents zinc (Zn), a divalent monoatomic cation of an alkaline earth metal selected from Group 2 of the IUPAC periodic table of the elements, or a divalent transition metal from groups 4-12 of the IUPAC periodic table of the elements, or a combination of zinc with a divalent monoatomic cation of an alkaline earth metal selected from Group 2 of the IUPAC periodic table of the elements, or a divalent transition metal from groups 4-12 of the IUPAC periodic table of the elements, or with any combination of such cations; M’’ represents a trivalent monoatomic cation of an element selected from Group 13 of the IUPAC periodic table of the elements, or any combination of such cations; M’’’ represents a monoatomic cation of an element selected from Group 14 of the IUPAC periodic table of the elements, or any combination of such cations; X represents an anion of an element selected from the halogens of Group 17 of the IUPAC periodic table of the elements, or any combination of such anions; X’ represents an anion of one or more elements selected from the chalcogens of Group 16 of the IUPAC periodic table of the elements, or any combination of such anions; and M’’’’ represents a dopant cation of an element selected from rare earth metals of the IUPAC periodic table of the elements, or from transition metals of the IUPAC periodic table of the elements, or of barium (Ba), strontium (Sr), thallium (Tl), lead (Pb), or bismuth (Bi), or any combination of such cations, or M’’’’ is absent; and a is a value of 0.001 – 4; b is a value of 0 – 10.5;c is a value from above 0 to 4; d is a value limited by d*c extending from above 0 to 2; n is a value from above 0 to 4.

2. The material according to claim 1, wherein M1’ represents sodium (Na) or potassium (K), preferably Na.

3. The material according to claim 1 or 2, wherein M2’ represents zinc (Zn) or a combination of Zn and magnesium (Mg), preferably Zn.

4. The material according to any preceding claim, wherein M’’ represents aluminium (Al).

5. The material according to any preceding claim, wherein M’’’ is silicon (Si).

6. The material according to any preceding claim, wherein X is chlorine (Cl).

7. The material according to any preceding claim, wherein X’ is sulphur (S).

8. The material according to any preceding claim, wherein M’’’’ is absent.

9. The material according to any preceding claim, having the following chemical formula (II): (Na8-2aZna)(Al14-(4b / 3)Sib)O24(Cl2-dcdSnc-) (II) 10. The material according to any preceding claim, wherein a is a value of 0.05 – 4, preferably 0.1 – 1.0, b is a value of 1 – 10, preferably 6, c is 2, d is a value of 0.04 – 0.1, and n is 2.

11. A method for synthesizing the material according to any preceding claim, by ^ mixing and grinding one or more reagents containing X, one or more reagents containing X’, one or more reagents containing M2’ and one or more reagents containing M1’, M’’and M’’’,^ mixing the components of the reagent mixture and optionally heating the mixture, to obtain a precursor, and ^ heating the precursor to 400–1300 ºC to obtain the final sensor material.

12. The method of claim 11, wherein the reagents containing X, X’ and / or M2’ are selected from molecules or salts of alkali metals, alkaline earth metals or transition metals with halogens or chalcogens, optionally containing oxide, preferably being selected from sodium chloride or bromide, potassium chloride or bromide, zinc chloride or bromide, magnesium chloride or bromide, or from the corresponding sulphates, for example by selecting sodium chloride (NaCl), sodium sulphate (Na2SO4) and zinc chloride (ZnCl2), typically in dried form.

13. The method of claim 11 or 12, wherein the minerals containing M1’, M’’ and M’’’ are selected from oxides, salts, minerals or other molecules containing M1’, M’’ and M’’’, preferably from zeolites, one example being Zeolite A.

14. The method of any of claims 11 to 13, wherein the amounts of reagents are selected based on the desired values for a, b, c and d of Formula (I) or (II).

15. The method of any of claims 11 to 14, wherein the components of the reagent mixture are mixed and thereafter optionally heated to a temperature of 400–1300 °C to obtain the precursor, preferably to a temperature of 650–750 °C, most suitably to a temperature of 680–720 °C, e.g. in an air atmosphere.

16. The method of any of claims 11 to 15, wherein the components of the reagent mixture are heated for 4–10h to obtain the precursor, preferably for 4–6h.

17. The method of any of claims 11 to 16, wherein the precursor is heated to a temperature of 650–750 °C, preferably 680–720 °C, typically for 1–3 h, preferably in a reducing gas atmosphere, for example in a H2 / N2 gas atmosphere, e.g. at a volume ratio of 0.8–1.2 / 8.8–9.2.security markers, counterfeit markers, or in smart films or smart windows, particularly in security devices, medical applications or diagnostic applications.

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